Star wheels are used on various types of automated handling lines to convey containers to and from, and within, various machines such as rotary packaging machines. In particular, star wheels are used to convey containers between rectilinear conveyors to a rotating machine part and back to a rectilinear conveyor. The star wheel may take a container from a conveyor such as screw feed and pass the container to a machine such as a washer, filler, capper or labeller. Sometimes, orientation of the container is important and the star wheel may assist in ensuring that the container adopts the correct orientation.
Star wheels derive their name from the shape of one of their type: members of this type are generally disc shaped and their periphery contains a plurality of recesses or pockets thereby forming an approximate star-shape. The star wheels rotate about a central axis.
As mentioned above, recesses may be provided in the peripheries of the discs to form pockets for receiving containers therein. The star wheel is positioned on an automated handling line so that a container travelling down the handling line is received within a pocket as the star wheel rotates. For example, this may be effected by synchronising rotation of the star wheel with that of a screw feed, such that the screw feed delivers containers to a pick up point as a pocket moves through the pick up point. The container is retained within (and hence conveyed by) the pocket as the star wheel rotates, often by virtue of a guide rail provided to face the periphery of the star wheel, before being passed on to a subsequent machine part at a defined hand off point. Containers are generally retained by the pocket supporting the container between a pair of contact surfaces that urge the container against a guide rail that encircles at least part of the star wheel's periphery.
Star wheels may be used with a variety of containers that include bottles, cans and tins, although it will be realised that this list is not exhaustive. Moreover, it is often the case that more than one type of container will be processed on any particular handling line. For example, it is common to process containers relating to different pack sizes of a product such as 35 cl and 70 cl drinks bottles. Accordingly, it is advantageous for a star wheel to be adjustable so as to accommodate different sizes of container and/or different shapes of container.
In addition to a general requirement to accommodate containers of differing shapes and sizes, it is often important to preserve the position of the opening of a bottle. For example, the container may be a bottle with a narrow neck that is presented to a filling machine that generally has a filler head located in a fixed position: when the bottle is presented to the filler head, the neck of the bottle must be on the correct path such that its opening passes exactly beneath the filler head. Thus, it is important that the star wheel conveys containers such that their openings follow a predetermined path.
In the past, each star wheel could only handle containers of a specific shape and size, and this meant having to change the star wheel each time a different container was introduced onto a handling line. This is undesirable as it is both time consuming and necessitates having to keep a stock of different-sized star wheels. Attempts have been made to overcome this problem.
EP-A-0,412,059 describes an adjustable conveyor comprising a star wheel with upper and lower tiers that each comprise a disc with a periphery having formed therein a plurality of recesses. The size and shape of these recesses is fixed, and they define part-circles. A container is received partly within each recess. A radially adjustable pushrod is also provided in each recess. The pushrod defines a pocket having a back joined to respective sides by angled faces. In a first position, a relatively large container is supported by the recessed discs and the pushrod. Adjustment for smaller containers is possible in that the pushrods may be pushed into their respective recesses. When the pushrod is extended into a recess, the recessed disc no longer supports the container. Instead the container is supported only by the pushrod.
However, the shape of the pushrod means that only two points of contact are provided to support the container, namely between the container and each of the angled faces at the back of the pocket. In addition, support is provided at only one level and this permits greater movement of the containers away from the vertical. Also, the shape of the pocket defined by the pushrod must complement the shape defined by the recesses in the disc. This constraint on the shape of the pocket means that it cannot be tailored to match closely the shape of a container: in fact, it must have a shape that allows it to accommodate a range of containers according to the pushrod's range of movement.
EP-A-0,355,971 describes an adjustable star wheel. Rather than having a recessed disc to provide pockets, the star wheel uses a plurality of radially-adjustable pushrods that are connected to pivoting fingers. Accordingly, each pocket is defined at its back by the end of the pushrod and at its side by the finger. As the pushrod is moved radially in and out, the finger pivots to assist in defining a correspondingly smaller or larger pocket. As such, the pocket only provides two points of contact to support a container, and these points of contact are provided at one level. By its vary nature, the pocket cannot be closely matched to the shape of a container to be accommodated in the pocket.
Japanese Patent Application No. 10-35879 describes a star wheel having a tier defined by a pair of stacked discs. Each disc is provided with a plurality of fingers. A corresponding number of pockets are defined by pairs of fingers: a finger from one disc forms one side of the pocket and a finger from the other disc forms the other side of the pocket. The two discs may be rotated relative to each other so as to change the width of the pocket. However, the shape of the pocket is a composite formed in part by one of the discs and in part by the other of the discs. As such, the shape cannot be tailored to match a container with which the star wheel is designed to work.